How did the attack at Fort Sumter create conflict between the north and the south?

Fort Sumter was a US Army garrison on a tiny island in Charleston harbour.

The Confederacy wanted to assert sovereignty over it, as it was part of South Carolina. Lincoln did not recognise the Confederacy and said he would defend his garrison from all attacks.

Confederate artillery then fired on the fort, Lincoln appealed for volunteer-troops, and the war was effectively on.

Because the Confederacy was not officially recognised in Washington, there was no actual declaration of war, and nor was there a peace treaty afterwards.

Fort Sumter is taken as the beginning of the war, and the armistice at Appomattox is taken as the end.